Planet Earth: a great magnet

Our planet is a giant magnet. You prove this each time you use a compass,
but beyond that probably don't notice it much. You may not think of
magnetism at all while viewing an
aurora, the beautiful light show of polar
skies. Or when your AM radio won't tune in, or when your power won't turn
on. But all these things are affected by Earth's magnetic field.

Earth's invisible magnetic field extends far out into space to form a
region we call the magnetosphere. The force of the
solar wind pushes on the
magnetosphere, squeezing in the Sunward side and stretching the night side
into a long tail (called the magetotail) that extends hundreds of thousands
of miles into space. As the solar wind flows past the magnetosphere, it
acts like a cosmic generator, producing millions of amps of electric
current. Some of this electric current flows into Earth's upper atmosphere
which can light up like a neon tube to create the mysterious aurora
(Northern and Southern Lights).

A diagram of the Earth's magnetic field, which near the Earth resembles
that of a bar magnet. Courtesy NASA.

There are many unique regions in and near Earth's magnetosphere: the bow
shock, magnetotail, radiation belts, and the ionosphere. Earth's magnetic
field acts like a shield to the supersonic solar wind. A shock wave
(called the bow shock), like that produced by supersonic aircraft, slows
and heats the solar wind. The magnetotail extends far away from Earth on
the nightside. It is in the magnetotail, that charged particles are
energized and directed toward the polar regions where they cause the aurora.

The First Major Discovery of the Space Age

The Van Allen Radiation Belts were discovered by Explorers 1 and 3
in 1958. More...

Over 98% of the charged particles from the Sun and from galactic cosmic
rays that strike Earth's magnetosphere are deflected by it! The Van Allen
Radiation Belts -- two doughnut shaped belts that surround the Earth --
trap the rest of the harmful particles, which bounce back and forth along
magnetic field lines between Earth's north and south magnetic poles like
beads on a wire.

In the upper part of Earth's atmosphere, right at the edge of Electric
Space, lies a charged layer of plasma and neutral gases called the
ionosphere. It extends from 50 to 300 miles above the surface of Earth.
Here, ultraviolet
rays from the Sun and high-energy particles from outer
space bombard the gases of our atmosphere. They collide with the atoms,
knocking off electrons and leaving the positively charged nucleii--called
ions--floating free. Because of these free-floating charged particles, the
ionosphere can conduct electricity. During disturbed conditions, huge
currents can flow which cause Earth's most spectacular light show: the aurora.

SPACE STORMS

Earth's magnetosphere is very sensitive to space weather. During the Sun's
most active periods, solar wind disturbances, created by
coronal mass ejections and
flares,
buffet Earth's magnetosphere and they can produce large
magnetic storms
lasting one or more days. Magnetic storms have been
known to seriously damage electric power networks, affect communications,
and damage satellites orbiting near Earth.